The inventive concept relates generally to electronic memory technologies. More particularly, certain embodiments of the inventive concept relate to methods for storing data in a nonvolatile memory device and methods for testing a nonvolatile memory device.
Most nonvolatile memory devices are subject to deterioration according to their usage. For example, flash memory devices tend to fail after a certain number of program or erase operations have been performed.
To cope with deterioration of individual memory cells, many nonvolatile memory devices or controllers include error correction circuitry that can overcome failures in a small number of memory cells. However, if the number of errors becomes relatively large, it may exceed the capability of the error correction circuitry and data may be lost.
To avoid losing data due to large numbers of errors, some nonvolatile memory devices keep track of failed memory cells, and take measures to protect data if the number of failed memory cells approaches a critical level. Unfortunately, such measures may be inadequate in the event that the failures follow an irregular pattern, e.g., where numerous memory cells become failed memory cells at approximately the same time.